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            height: 50px;
            width: 100px;
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            text-align: center;
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<body>


<ul>
    <li id="l1">
        章节
        <ul id="u1">

            <li>
                思想品德
            </li>
            <li>
                毛泽东理论
            </li>
            <li>
                马克思思想
            </li>
        </ul>
    </li>
    <li>问答</li>
    <li>笔记</li>
    <li>提问</li>
</ul>


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